In many applications (such as AC motor control with current measurement in the phase nodes), sigma-delta analog digital converters (ADCs) are often used because they allow a cost effective isolation of the data streams (they do not refer to the same ground potential).
Although in such applications similar sensors (shunts) are used, a later analog treatment and filtering (e.g. by amplifiers or passive components with tolerances) can lead to a mismatch in the delay between the measurement channels. This leads to the effect that the conversion results do not relate to the same point in time.
If the input signals are converted and the results are used in combination with other signals (e.g. another input signal or a reference signal), the mismatch in the delay leads to an undesired reduction of the ENOB value of the converters (ENOB=effective numbers of bits which can be considered as resolution of the converter).
In the case that different sensor types are used (e.g. voltage and current sensors for power meters), it is also very important to take conversion values that correspond to the same point in time. However, using different sensor types may already lead to a significant delay mismatch.
In telecommunication, such effects are solved by later numeric treatment of the conversion results, because in this field, equivalent computation is done anyhow.
In AC motor control and other applications, especially for low-cost consumer markets, the computing power to solve this problem in a numerical way is not available. As a result, a simple mechanism to minimize the delay mismatch before using the results is advantageous. Furthermore (and contrary to telecommunication applications), in AC motor control, each conversion result is not necessarily taken into account, but only those values are of interest that are located in a defined measurement window (e.g. synchronized to a PWM signal).
Therefore, there exists a need for a method and a system for minimizing delay mismatch between two measurement channels that is simple and cost effective.